When you register online the website will ask you which team you want to join, units I am unsure of. Pack what you would normally bring to the field with the exception of A LOT of Batteries and water. If you have backup gear that you don't normally bring to the field because you don't need it or your field is close BRING IT. You will want that spare loader that you left on the kitchen table when yours breaks down. Now if you don't have spare gear, not to worry just take good care of your stuff and make sure it works FLAWLESSLY before you get there; A small leak at home will be 3000psi in the scenario game when you are in the woods for hours at time. In addition to your paintball gear, bring a DIFFERENT bag with your clothes which should include, Paintball (or BDUs/ whatever you use), non-cotton socks, Dry-fit shirt, Jersey/ over shirt, boots or cleats(I prefer cleats for the grip and boots for the ankle support unless you get mid length cleats ie. Landsharks), PADS, underwear. And don't forget a lot of WATER.

To choose your side, you must pre-register. During the pre-registration you get to choose Team (New Empire or Horde) and Legion or Tribe (i.e. New Empire Pegasus Legion or, Horde Vandals), Alternatively, you can simply pick a side (Empire or Horde) and let the CPX / LL place you where you're needed.

As for specialists, they are assigned by your side's leadership. The available positions are listed and described in the Rules which, I strongly suggest you read and ask questions here if you aren't clear.

As for packing, I suggest you review the "Living Legends Packing List / Info guide (requires a google login to access it) stickied in the top of this section or, the "Comprehensive Guide To Living Legends" stickied as well. The comprehensive guide also provides good information on what to expect when you get there, and some general preparations. Both of these guides were put together by players here after several years of Living Legends experience.